DESCRIPTION: Tumor necrosis factor-alpha (TNF) influences a wide variety of cellular functions, including cell growth, cell death and metastases. Although the action of TNF is mediated through its cell surface receptors, the intracellular events that link ligand binding to the cytotoxic action of TNF remain elusive. The overall objective of this grant application is to define the signaling mechanisms that regulate TNF-mediated cell killing. Signaling through TNF receptors (TNFR) is unique. They do not possess any intrinsic kinase activity. It is presumed that upon ligand binding TNFR activate and/or recruit other factors or kinases to convey its signal. The specific focus of this project is to define the functional significance of protein phosphorylation and dephosphorylation in TNF signaling. TNF inhibits the growth of breast cancer cells in vitro but little is known regarding the involvement of TNF in breast cancer pathogenesis. The protein kinase C signal transduction pathway appears to regulate TNF sensitivity in breast cancer cells. The specific aims of this application are to determine the contribution of PKC isozymes in TNF-mediated cell death, to study the regulation of TNFR function by kinases, to investigate their involvement on the down-stream signaling events of TNF and to determine the basis for TNF resistance in normal and malignant mammary cells.